Air seed meters have been known in the art for some time. One current commercial air seed meter uses an enclosure for the disc having a first housing section forming a reservoir for the seeds and receiving and enclosing the seed side of the disc, and a second housing section, connected to the first housing section for contacting and enclosing the vacuum side of the disc. The second housing section forms a vacuum chamber, in the case of an air meter employing suction to secure the seeds to the disc.
In most cases, two housing sections form the overall meter casing, are in the form of flat, circular end walls (i.e. disc-shaped) with generally cylindrical side walls. The housing sections or halves are mounted with the centers of the end plates concentric with the axis of rotation of the disc. Moreover, in prior art meters, for the most part, a seal is formed between the vacuum cover and the seed disc.
The seed disc is driven typically for rotation about a generally horizontal axis. As the disc, having spaced seed apertures located circumferentially about the disc, is rotated through the seed reservoir, seeds are picked up and attached to an aperture by means of a pressure differential between the seed reservoir and the vacuum chamber. The seeds are held to the disc by the pressure difference as they pass through the seed reservoir. The seed is passed to a discharge area which, typically, is located adjacent a downwardly facing chute formed as a tangential channel in the meter housing.
In prior art air seed meters which seek to establish a seal between the vacuum housing and the rotating disc, the seal extends around the periphery of the portion of the vacuum housing which forms the actual vacuum chamber. That is, a portion of the vacuum chamber typically is devoted, in prior art devices, to a point for releasing the seeds sequentially into the discharge chute. This is done, in some cases, by having the seeds pass into a region adjacent the discharge chute. The “vacuum” (i.e. lower pressure) side of the disc, as it passes adjacent the discharge chute, naturally is exposed to air pressure near, but not always at atmospheric levels.
There are some difficulties associated with such arrangements. First, it is desirable to establish atmospheric pressure at the actual point of discharge. For example, the higher the air pressure differential across the seed disc at the moment of discharge, the less would be the tendency to release the seed at the same location accurately. Any variation in the pressure differential across the seed disc at the intended point of release, will create variances in the spacing of the seeds upon discharge and deposit into the seed furrow. According to these structures, it became necessary, in some cases, to create an elaborate sealing mechanism which defined only the boundary of the vacuum chamber and excluded the region of release adjacent the discharge chute.
Still further problems existed in that a “chimney effect” may be created in the discharge chutes of some existing meters. By this it is meant that as seed is routed to the release point in the discharge chute, it will be appreciated that the reservoir side of the seed disc is at approximately atmospheric pressure; and if measures are not taken, the interior of the seed reservoir may be at a slightly sub-atmospheric pressure. This also increases the likelihood that air is drawn up the discharge chute (i.e. if the reservoir is at a pressure even slightly below atmospheric), resulting in a “chimney effect”or updraft of air in the discharge chute and requiring compensation. The chimney effect not only reduces the reliability of accurate seed release, and therefore spacing, but depending upon the velocity of air flowing in a reverse direction in the seed discharge chute, it might alter the discharge flight path of the seed, thereby further affecting the fall time (and ultimate spacing) of seeds.
Some prior art seed discs which use recesses or “cells” in the surface of the disc to capture and seat seeds experience another source of possible inconsistent or unequal seed spacing upon delivery to the furrow. Specifically where the seed is required to move axially of the disc (i.e. parallel to the axis of rotation) to release, there is an increased tendency for the seed to strike the wall of the discharge chute and to ricochet off the walls of the chute and to be delayed in release from the cell. This effect creates variation in the length of seed travel (and thus variations in delivery time) from release to deposit, and thus results in inconsistency in seed spacing in the furrow.
Other seed discs, which do not have recesses or depressions in the seed disc for retaining seeds, require the use an auxiliary device, some shaped like a spider with wire legs, to agitate and bring the seeds in the reservoir up to the speed of the disc to facilitate seating of the seeds on the disc.
Another difficulty with such prior art air meters as described above, is that for the most part, the seal between the disc and the vacuum housing is generally a circular path centered on the axis of rotation of the disc and located at the perimeter of the disc. In such structures, the portion of the disc engaging the circular seal tends to create a narrow annular region of engagement between the seal member and the disc or seal, thus creating a narrow band of wear on the disc. This wear “ring” creating wear on the disc or seal, results in a variance between the surface of the disc which was attempted to be sealed and the contact surface of the seal, thus reducing the effectiveness of some seals.
Moreover, such prior art structures rendered it difficult to clear the interior of the vacuum chamber as well as the exterior from fine particles, dust, dirt and chips or broken segments of seeds that may have cracked (collectively referred to as “debris” or “fines”). Such particles could pass through or obstruct the apertures in a seed recess and may even accumulate between contacting surfaces where it was difficult, due to the nature of some prior devices, to clear the debris. Some prior art devices, such as disclosed in U.S. Pat. No. 6,247,418, created tiny slots between a seal of the vacuum housing and the disc so that air could flow across the seal through the groove in the adjacent surface of the disc between the contact surfaces to clear the disc and seal surface of fine particles. However, the cross section of such slots tended to reduce, with diminished clearing effect, as the sealing member wore into the surface of the disc, thereby reducing the dimensions in and effectiveness of the clearing passageways.